Mass killer Anders Breivik has been indicted on terror and murder charges for the deaths of 77 people in a bomb and shooting rampage, but prosecutors said he is unlikely to go to prison.

They consider the 33-year-old right-wing extremist psychotic and will seek a sentence of involuntary commitment to psychiatric care instead of imprisonment, unless new information about his mental health emerges during the trial set to start in April.

As expected, they charged him under a paragraph in Norway's anti-terror law that refers to violent acts intended to disrupt key government functions or spread fears in the population.

Breivik has confessed to the July 22 attacks but denies criminal guilt, portraying the victims as "traitors" for embracing immigration policies he claims will result in an Islamic colonisation of Norway.

The indictment listed the names of the eight people killed when a bomb exploded in Oslo and the 69 victims of a shooting spree on Utoya island outside the capital, where the youth wing of the governing Labor Party was holding its annual summer camp.

Reading from the indictment, prosecutor Inga Bejer Engh said 34 of the victims at Utoya were between 14 and 17 years old, 22 were aged 18-20, six were between 21 and 25 and seven were older than 25. She said 67 died of gunshot wounds, and two died of fall injuries or drowning. The indictment also listed the names of 33 people wounded in the shooting and nine people who were seriously injured by the explosion in Oslo's government district.

Police spokesman Tore Jo Nielsen said outside Oslo's Ila prison that Breivik had been "totally calm" when he was read the charges.

The terror charges carry a maximum penalty of 21 years in prison but prosecutors are working under the assumption that Breivik is legally insane and therefore unfit for prison. However, they said that this assessment could change during the trial.

"We're keeping the possibility open that there could be things during the presentation of evidence that may change our view," Ms Bejer Engh said.

A second, court-ordered psychiatric evaluation of Breivik is ongoing after an initial review - which concluded he was a paranoid schizophrenic - met widespread criticism. Some experts questioned whether someone suffering from a grave mental illness would be capable of carrying out attacks requiring such meticulous preparation.